Since then the column has covered albino wildflowers, droughts, floods, walking sticks, coral snakes, the ozone layer, volcanoes, honeybees, Mexican smoke, computers, mockingbirds, African and Chinese dust and the weather during the siege of the Alamo.

These and many other topics have resulted in hundreds of questions and comments from readers.

Many questions concern the identification of flowers, plants, insects and birds. When the column was new, very few identification questions were accompanied by photographs. Now photos are commonly sent, some of which are quite good.

When I cannot answer an identification question, the usual response is to inform the reader that the name of an unknown plant or animal can often be found by entering key words into the search window of various plant and wildlife organizations.

Texas Parks & Wildlife and Texas A&M University have considerable information about Texas species. The Cornell Ornithology Lab is among the best sites for identifying birds. Internet search engines are ideal for finding sites like these. Google's image option is especially helpful.

Another class of popular questions concerns how to eliminate unwanted insects and plants. Not being trained and certified in these areas, I usually recommend that the writer contact a professional or search the Internet for suggestions. Often I note that pesticides can have unintended consequences, like killing walking sticks and fireflies when wasps were the prime target.

Occasionally a topic is not well received. For example, some people believe that contrails painted across the sky by high-flying jets are malevolent "chemtrails" designed to reduce the population. A column that debunked this idea drew a sharp rebuke from a chemtrail believer. He was unimpressed when I explained I had made scientific measurements of contrails and published the results.

So far the most memorable message from a reader remains one mentioned in a few prior columns.

An elderly gentleman rejected my explanation for the bright light over the horizon he was observing in the evening. He firmly insisted that the light was a UFO and not the planet Venus, which I was also watching.

Some readers address their notes to "Dr. Mims," so it's necessary to explain to them (and to remind regular readers) that my academic background is a bachelor's degree in government with minors in history and English.

The science from which I earn a living was not learned in a classroom but at an electronics workbench, through a microscope and from 22 years of monitoring sunlight, haze and the ozone layer with homemade instruments.